Palladium Sites Research Articles

Enhanced Radical Dehydrogenation over Carbon Monoxide-Decorated Palladium Sites for Linear α-Olefin Production from Biomass-Derived Fatty Acids

Enhanced Radical Dehydrogenation over Carbon Monoxide-Decorated Palladium Sites for Linear α-Olefin Production from Biomass-Derived Fatty Acids

Activating CoP via spontaneous atomic palladium doping for efficient hydrogen evolution

Electrocatalytic hydrogen evolution is an efficient and clean hydrogen production technology with simple process and high product purity. Searching for inexpensive alternatives to platinum will help popularize proton exchange membrane water electrolysis (PEMWE) technology. However, the alternative catalytic materials are essentially limited by low catalytic efficiency. Herein, we address this challenge through chemically activating cobalt phosphide (CoP) by doping a small amount of atomic palladium. Palladium substitution occurs at the cobalt site of CoP. Theoretical calculations manifest that the phosphorus atoms near the palladium sites exhibit almost zero hydrogen adsorption free energy. The final cobalt phosphide doped with only 2 wt% of palladium shows wonderful HER performance. Specifically, its overpotential at a current density of 10 mA cm−2 is only 37.5 mV in an acidic medium, and the corresponding Tafel slope is 56 mV dec−1. This work provides a reference for preparing high performance non-platinum catalysts.

Highly ordered Periodic Mesoporous Organosilica material containing the ionic 4,4-bipyridinium group and decorated with palladium nanoparticles: A proposal for nanoreactor

A Periodic Mesoporous Organosilica (PMO) containing the cationic 4,4-bipyridinium group, presenting 0.25 mmol g−1 that corresponds to 11.5 w/w%, was successfully prepared. This material was designed to have the ionic group acting as anchoring agent of PdCl42- anion complex, in a much lower amount than the available cationic sites (3 and 15 molar%). Subsequently, the palladium complex was in situ reduced to obtain stabilized palladium nanoparticles (PdNP). The ensemble of characterization results showed that the PMO material walls have a cylindrical morphology with hexagonal packing, generating well-ordered pores with a narrow size distribution and high surface area, even after being decorated with PdNP. This material is a candidate to be an efficient nanoreactor considering that it contains spatial uniformity in its chemical sites and confined environment. Aiming to evaluate the availability of palladium sites, the material was used as a catalyst in the reduction of p-nitrophenol model reaction. Although the catalyst of the present study has a comparable activity with other already reported systems, it presents the impressive lowest molar palladium/p-nitrophenol ratio found in literature.

Construction of highly active photocatalytic interfaces through light field modulation and photo-deposition of Pd sites

Anchoring noble metal sites through photo-reduction is an effective way to modulate charge distribution on photocatalytic interfaces, thereby enhancing photocatalytic performance. The irradiation field on the exposed surfaces of photocatalysts has an important influence on the morphology and distribution of noble metal sites. However, non-uniform light field derived from the scattering effects of particle-form photocatalysts hinders the well-distributed photo-deposition of noble metal sites. To address this challenge, we proposed a photo-deposition method utilizing the optical fiber coated with photocatalysts. TiO2 nanorod (NR) array was coated on the optical fiber to achieve a well-distributed irradiation filed across the NR array. This resulted in a concentration of the irradiation field primarily within the NR array, maintaining uniformly distributed light intensities throughout. Palladium (Pd) sites dominated by nanoclusters were well distributed on TiO2 NR array utilizing a photo-reduction method. These Pd sites functioned as electron acceptors, facilitating the effective separation and transfer of photo-generated carriers. Consequently, an highly active photocatalytic reaction interface was constructed, demonstrating the accumulation of a substantial concentration of holes and their efficient conversion into hydroxyl radicals (·OH). Notably, hydroxyl radicals with a concentration of 62.6 μM could be generated within 14.4 min. The construction of this efficient photocatalytic interface offers an optimal platform for accelerating photocatalytic reactions and enhancing photocatalytic efficiency.

Novel synergistically effects of palladium-iron bimetal and manganese carbonate carrier for catalytic oxidation of formaldehyde at room temperature

The elimination of formaldehyde at room temperature holds immense potential for various applications, and the incorporation of a catalyst rich in surface hydroxyl groups and oxygen significantly enhances its catalytic activity towards formaldehyde oxidation. By employing a coprecipitation method, we successfully achieved a palladium domain confined within the manganese carbonate lattice and doped with iron. This synergistic effect between highly dispersed palladium and iron greatly amplifies the concentration of surface hydroxyl groups and oxygen on the catalyst, thereby enabling complete oxidation of formaldehyde at ambient conditions. The proposed method facilitates the formation of domain-limited palladium within the MnCO3 lattice, thereby enhancing the dispersion of palladium and facilitating its partial incorporation into the MnCO3 lattice. Consequently, this approach promotes increased exposure of active sites and enhances the catalyst's capacity for oxygen activation. The co-doping of iron effectively splits the doping sites of palladium to further enhance its dispersion, while simultaneously modifying the electronic modification of the catalyst to alter formaldehyde's adsorption strength on it. Manganese carbonate exhibits superior adsorption capability for activated surface hydroxyl groups due to the presence of carbonate. In situ infrared testing revealed that dioxymethylene and formate are primary products resulting from catalytic oxidation of formaldehyde, with catalyst surface oxygen and hydroxyl groups playing a crucial role in intermediate product decomposition and oxidation. This study provides novel insights for designing palladium-based catalysts.

Transfer Hydrogenation with a Carbon‐Nitride‐Supported Palladium Single‐Atom Photocatalyst and Water as a Proton Source

AbstractSolar‐driven transfer hydrogenation of unsaturated bonds has received considerable attention in the research area of sustainable organic synthesis; however, water, the ultimate green source of hydrogen, has rarely been investigated due to the high barrier associated with splitting of water molecules. We report a carbon‐nitride‐supported palladium single‐atom heterogeneous catalyst with unparalleled performance in photocatalytic water‐donating transfer hydrogenation compared to its nanoparticle counterparts. Isotopic‐labeling experiments and operando nuclear magnetic resonance measurements confirm the direct hydrogenation mechanism using in situ‐generated protons from water splitting under visible‐light irradiation. Density functional theory calculations attribute the high activity to lower barriers for hydrogenation, facilitated desorption of ethylbenzene, and facile hydrogen replenishment from water on the atomic palladium sites.

Transfer Hydrogenation with a Carbon-Nitride-Supported Palladium Single-Atom Photocatalyst and Water as a Proton Source.

Solar-driven transfer hydrogenation of unsaturated bonds has received considerable attention in the research area of sustainable organic synthesis; however, water, the ultimate green source of hydrogen, has rarely been investigated due to the high barrier associated with splitting of water molecules. We report a carbon-nitride-supported palladium single-atom heterogeneous catalyst with unparalleled performance in photocatalytic water-donating transfer hydrogenation compared to its nanoparticle counterparts. Isotopic-labeling experiments and operando nuclear magnetic resonance measurements confirm the direct hydrogenation mechanism using in situ-generated protons from water splitting under visible-light irradiation. Density functional theory calculations attribute the high activity to lower barriers for hydrogenation, facilitated desorption of ethylbenzene, and facile hydrogen replenishment from water on the atomic palladium sites.

Partial oxidation of methane to oxygenates by oxygen transfer at novel lattice oxygen sites of palladium and ruthenium bimetal oxide

Alumina-supported bimetal oxide (PdRuOx) catalysts were prepared by galvanic displacement reduction method for partial oxidation of methane into oxygenates, and evaluated in a fixed-bed reactor at relatively low temperatures of 280–310 °C, using a mixture of NO and O2 as the oxidant. The bimetal oxide catalysts exhibited high selectivity to HCHO. However, CO2 was dominantly obtained over two alumina-supported monometal oxide (PdO and RuO2) catalysts. Characterizations results showed that bimetal oxide-PdRuOx species with Pd-(O)-Ru active sites can selectively convert CH4 to HCHO through the transfer of its novel lattice oxygen. And in this process, CH3OH may play as an intermediate. Compared to oxidation with either O2 and NO, the mixture oxidant of NO and O2, acting as an oxygen shuttle through the gas-phase reaction of NO+1/2 O2→NO2, promoted the selective formation of HCHO.

Conversion of dimethyl ether to liquid hydrocarbons over the nano‐Pd‐ZnHZSM‐5 catalyst obtained by laser electrodispersion of the metal

AbstractBACKGROUNDPalladium particles with a size of 2 nm were obtained by laser electrodispersion (LED) and used to prepare the Pd‐ZnHZSM‐5(LED) catalyst (Pd = 0.0005 wt%). The deposition of the LED palladium particles on the surface of ZnHZSM‐5 provided a high dimethyl ether (DME) conversion into liquid hydrocarbons; the percentage of the unreacted intermediate (methanol) decreased by an order of magnitude and the selectivity for i‐alkanes increased (more than 80 wt%). The Pd‐ZnНZSM‐5(LED) catalyst showed higher activity and selectivity than the traditional Pd‐ZnНZSM‐5 catalyst (impregnation).RESULTSThe features of the catalytic action of Pd‐ZnHZSM‐5(LED) are associated with the high density of nanosized Pd0 and Pd2+ phases on the ZnHZSM‐5 surface. The LED particles are immersed in the surface of the zeolite to a maximum depth of 0.5 nm and do not penetrate deep into the pores of the zeolite. In Pd‐ZnНZSM‐5(LED), the zinc sites and palladium sites are separate. On Brønsted acid sites and zinc sites in the micropores of the zeolite occure target reactions. Part of arenes and unreacted alkenes exit the pores of zeolite are hydrogenated on the palladium. The product obtained on Pd‐ZnHZSM‐5(LED) is characterized by a high content of i‐alkanes (more than 80 wt%) and a low content of arenes (no more than 5 wt%).CONCLUSIONThe results demonstrate the high promise of the LED method for the preparation of high‐performance catalysts with ultra‐low content of noble metal for conversion of oxygenates to synthetic liquid hydrocarbons with a high yield of i‐alkanes and low yield of arenes. © 2022 Society of Chemical Industry (SCI).

Au-Pd separation enhances bimetallic catalysis of alcohol oxidation.

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications1-3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde4 but are less effective for oxygen reduction5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity isoften limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladiumcatalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect-a cooperative redox enhancement-offers an approach to the design of multicomponent heterogeneous catalysts.

Nanoglobular carbon and palladium–nanoglobular carbon catalysts for liquid-phase hydrogenation of organic compounds

The results of studies related to the development of synthesis, determination of formation conditions and elucidation of the mechanism of palladium–carbon catalyst action are integrated and critically analyzed. The attention is focused on Pd/NGC compositions (NGC is nanoglobular carbon). Methods for NGC preparation with an emphasis on its most common form, carbon black, are considered. The following issues are addressed: mechanisms of formation of carbon nanoglobules and their aggregates, methods of varying the size of nanoglobules, functionalization of the NGC surface to make it suitable as a support for palladium nanoparticles, views on the formation mechanism of palladium clusters and nanoparticles on the carbon support surface and effect of the structure and surface chemistry of carbon nanoglobules on the state of palladium sites in Pd/NGC compositions. The published data on selective hydrogenation of organic compounds in the presence of Pd/NGC catalytic compositions are integrated and systematized. The catalytic properties of Pd/NGC are analyzed in comparison with the properties of palladium catalysts supported on other carbon materials (activated carbon, carbon nanotubes). The influence of preparation conditions of NGC-based palladium compositions on their catalytic properties in practically important hydrogenation reactions is discussed. Promising trends for further research on the development of molecular design methods, study of the genesis of Pd/NGC compositions and extension of their applications in hydrogenation processes are considered.The bibliography includes 623 references.

Single palladium site in ordered porous heteroatom-doped carbon for high-performance alkaline hydrogen oxidation

Alkaline exchange membrane fuel cells are impeded by the lack of cost-effective, highly efficient catalysts for the sluggish hydrogen oxidation reaction (HOR). Herein, single-atomic Pd sites supported by ordered porous N,S-doped carbon are synthesized, exhibiting remarkable alkaline HOR performance. This catalyst exhibits an ultrahigh anodic current density and mass-specific kinetic current of 2.01 mA cm–2 and 27,719 A gPd–1 (at an overpotential of 50 mV), respectively, not only outperforming the Pt/C counterpart but also making it among the best reported HOR catalysts. Furthermore, this catalyst exhibits a negligible activity decay during long-term electrolysis and a good CO tolerance capability. Experiments and theoretical calculations indicate that the synergistic effect from single Pd sites and heteroatom doping (N and S) weakens the binding energy of Had intermediates, thereby accounting for its superior HOR activity. This study provides a guideline for developing single-atomic site catalysts for highly efficient, stable alkaline HOR.

Charge transport variation from Bloch\u2013Gr\xfcneisen to Mott variable range hopping and transport change due to hydrogenation in Palladium thin films

We report a systematic investigation of the differences in charge transport mechanism in ultra-thin nano-island like films of palladium with thickness varying between 5 nm and 3 nm. The thicker films were found to be metallic in a large temperature range with a dominant Bloch–Grüneisen mechanism of charge transport arising due to electron-acoustic phonon scattering. These films were also found to exhibit an additional electron–magnon scattering. At temperatures below 20 K, the two films displayed a metal-insulator transition which was explained using Al’tshuler’s model of increased scattering in disordered conductors. The thinner films were insulating and were found to exhibit Mott’s variable range hopping mechanism of charge transport. The thinnest film showed a linear decrease of resistance with an increase in temperature in the entire temperature range. The island-like thin films were found to display very different response to hydrogenation at room temperature where the metallic films were found to display a decrease of resistance while the insulating films were found to have an increase of resistance. The decrease of resistance was ascribed to a hydrogen induced lattice expansion in the thin films that were at the percolation threshold while the resistance increase to an increase in work function of the films due to an increased adsorption of the hydrogen atoms at the surface sites of palladium.

OPTIMIZATION OF VINYL ACETATE PRODUCTION PROCESS

In the article, the kinetic laws and kinetics and mechanism of the oxidation acetylationreaction of ethylene in the vapour phase were studied in detail in a catalyst containing0,4%Рd+4%Cu+7%CH3COOK/HSZ. It was found that the total rate of the reaction was proportionalto the amount of unmodified and modified active sites of palladium (not clusters). Excess amountsof the modifier (both potassium acetate and copper) have been shown to block active sites byreducing catalyst efficiency.

Carbon Molecular Sieve Supported Pd Catalyzed Hydrogenation of Cinnamaldehyde in Alkaline Medium

Synthesis of various fine chemicals and pharmaceuticals are regulated through selective hydrogenation of α,β-unsaturated aldehydes. Hydrocinnamaldehyde is one of the important compounds in perfumery and flavouring industries. It is highly precarious and challenging to control the product selectivity as well as conversion in cinnamaldehyde hydrogenation. In this study, an effective hydrogenation of cinnamaldehyde was attained in presence of aqueous-protic organic medium by utilizing Pd/CMS and other additives of alkali such as K2CO3. The Pd/CMS catalyst along with alkali media catalyzed the hydrogenation of C=C selectively in cinnamaldehyde in order to form hydrocinnamaldehyde with 100% conversion rate. Additionally, the parallel hydrogenation of C=O and C=C bonds in cinnamaldehyde takes place in absence of media. The C=O bond reduction in cinnamaldehyde can be restricted through K2CO3 addition to aqueous-protic solution. The active sites of palladium were found to be uniform and analyzed using HRTEM data. Based on the mechanism involved in micropores of carbon molecular sieves, the key role of promoter is associated with hydrogenation of cinnamaldehyde. The catalytic criterion was appropriate with the acquired activity data.

Structure-dependent regioselectivity of a roll-over cyclopalladation occuring at 2,2′-bipyridine-type ligands

In this work, different bipyridine-analogue ligands bearing a dimethylamino group in the meta-position of one of the heterocyclic rings were synthesized and reacted with palladium(II) acetate under identical conditions. Cyclometallated palladium(II) complexes with C,N- or C,N,N’-coordinating chelate ligands are formed which were characterized by elemental analysis, 1H and 13C NMR spectroscopy, and single crystal X-ray diffraction analysis. In the case of the mononuclear, C,N,N’-coordinated complex, which is formed by an attack of the palladium(II) site at of the N-methyl groups, the primarily coordinating acetato ligand is exchanged against a chlorido ligand, which is liberated from the solvent dichloromethane by a nucleophilic substitution reaction. In contrast, cyclometallation occurring at one of the six-membered heterocycles leads to dinuclear acetato-bridged palladium(II) complexes.

Modulating Single-Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis.

The electrochemical reduction of N2 to NH3 is emerging as a promising alternative for sustainable and distributed production of NH3 . However, the development has been impeded by difficulties in N2 adsorption, protonation of *NN, and inhibition of competing hydrogen evolution. To address the issues, we design a catalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2π* coupling between Pd and adsorbed N2 , leading to enhanced chemisorption and activated protonation of N2 , and suppressed hydrogen evolution. As a result, the catalyst achieves a high Faradaic efficiency of 24.8±0.8 % and a desirable NH3 yield rate of 69.2±2.5 μg h-1 mgcat. -1 , far outperforming the individual single-atom Pd catalyst. This work paves a pathway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.

Modulating Single‐Atom Palladium Sites with Copper for Enhanced Ambient Ammonia Electrosynthesis

AbstractThe electrochemical reduction of N2 to NH3 is emerging as a promising alternative for sustainable and distributed production of NH3. However, the development has been impeded by difficulties in N2 adsorption, protonation of *NN, and inhibition of competing hydrogen evolution. To address the issues, we design a catalyst with diatomic Pd‐Cu sites on N‐doped carbon by modulation of single‐atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d‐2π* coupling between Pd and adsorbed N2, leading to enhanced chemisorption and activated protonation of N2, and suppressed hydrogen evolution. As a result, the catalyst achieves a high Faradaic efficiency of 24.8±0.8 % and a desirable NH3 yield rate of 69.2±2.5 μg h−1 mgcat.−1, far outperforming the individual single‐atom Pd catalyst. This work paves a pathway of engineering single‐atom‐based electrocatalysts for enhanced ammonia electrosynthesis.

In-situ confinement of ultrasmall palladium nanoparticles in silicalite-1 for methane combustion with excellent activity and hydrothermal stability

Maximizing the use of palladium without compromises in catalytic activity and stability in the combustion of methane is extremely challenging due to the harsh operation conditions. To achieve this goal, a series of core-shell-structured catalysts with different amounts of palladium nanoparticles confined in hydrophobic silicalite-1 (Pd@S-1) was designed. Unexpectedly, a volcanic trend between catalytic activity and palladium loading was found as the loading increased from 0.3 wt% to 1.6 wt%, among which the 0.6 wt%Pd@S-1 exhibited the highest catalytic activity with a complete combustion temperature of 380 °C. Besides, the 0.6 wt%Pd@S-1 showed an ultrahigh stability in the high temperature applications due to the spatial confinement of palladium inside the rigid zeolite matrix. Moreover, owing to the hydrophobicity of the pure silica zeolite, the Pd@S-1 could selectively hinder the diffusion of water vapor into the palladium sites, leading to the outstanding water-resistance ability.

Synthesis of Pd/C Catalysts: Approaches to Regulating the Structure of Active Sites toward Achieving High Selectivity in Hydrogenation of Organic Compounds

The methods for regulating the physicochemical and catalytic properties of Pd/C compositions by varying their synthesis conditions were reviewed. The effect of the nature of the carbon support, the composition of the palladium precursor and its reduction conditions, and the addition of a second active metal on the formation of palladium sites, their dispersion, electronic state, and catalytic properties in practically important hydrogenation reactions was demonstrated using the results obtained by the authors. These data may be useful for the development of Pd/C catalysts exhibiting high activity and selectivity in the hydrogenation reactions of polyfunctional organic compounds.